Crosslinked polymers in which a water-retention amount is increased by a method of altering and optimizing an amount of polymerization initiators, polymerization temperature and polymerization concentration, and the like, and by a method of using chain transfer agents such as thiol have been proposed (see JP3-179008A). Furthermore, a large number of crosslinking polymers in which absorbing performance or liquid permeability of a swollen gel under loading is enhanced by, for example, a method of treating the vicinity of the surface of polymer particles have been proposed (see Japanese Patent No. 3118779, EP618005A, etc.).
In absorbent articles such as disposable diapers, there is a problem in that when a load is applied, for example, when a user sits down or lies down while wearing such an article, the absorption amount and the absorption speed lower, and as a result, leakage, etc. may occur. Therefore, there have been strong demands for absorbent articles that are free from such a problem and have high absorbing performance regardless of the users' state (even under loading).
That is to say, it is an object of the present invention to provide a water absorbing agent that can be used for absorbent articles that exert high absorbing performance under any conditions (even under loading), a process for its production, and absorbers and absorbent articles made by the water absorbing agent.
The present inventors have investigated in order to achieve the above-mentioned object and have found that the above-mentioned problems can be solved by taking the following points <1> to <3> into consideration:
<1> the water-retention amount after being soaked in a physiological saline for one hour;
<2> the absorption amount of a water absorbing agent after being soaked in a physiological saline under loading of 0.9 psi for one hour; and
<3> liquid permeation speed of a water absorbing agent after being soaked in a physiological saline under loading of 0.3 psi (20 g/cm2) for one hour.